A female shark gave birth to two baby sharks the other day at a Detroit aquarium. The interesting part is that the mother shark had not been in the presence of a male shark in over six years! How did it happen?
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The births have raised questions among scientists as to whether sharks may be able to reproduce parthenogenetically, a mode of reproduction in which the egg is not fertilized....
"Parthenogenesis has been documented in many reptiles," said Sweet. "There are at least five or six species of snakes, and it's been known in salamanders, lizards, and even a breed of turkeys. But any way you look at it, this is strange."
There are possibilities other than parthenogenesis. The Belle Isle white spotted bamboo shark may have been fertilized by a male at a very young age. However, although there have been some random reports of shark species storing sperm for a couple of months or more, six years is a long time, and Sweet thinks in this case it's extremely unlikely.
"We received both of these bamboo sharks from hobbyists, who don't typically keep breeding groups; for one thing their tanks aren't big enough. Usually hobbyists can only buy one egg here and there, and the eggs are typically imported as fertilized eggs. Both the hobbyists who donated these sharks only had one individual. I'm almost dead sure we can rule out long-term sperm storage."
A third possibility is that the Belle Isle bamboo shark is a hermaphrodite, harboring both male and female sex organs, and capable of fertilizing its own eggs.
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